In general, as handoff for mobile Internet Protocol (IP), there are Intra-subnet handoff, Inter-subnet handoff, and Inter-router handoff (“IP-based next-generation wireless networks”, Jyh-Cheng & Tao Zhang, John Wiley & sons Inc., 2004). Among them, the Inter-subnet handoff in which a jurisdictional address area of a router is changed and the Inter-router handoff correspond a case in which a moving mobile node (MN) requires a new IP subnet address. When an MN moves an adjacent cell belonging to the same router, since the Intra-net handoff uses the same IP subnet address, IP handoff does not occur. That is, when an MN visits from a mobile IP network to another region of an IP address area, a foreign agent (FA) acting as a virtual router in an external network gives a care-of address (CoA) to the MN. In this case, the MN registers the CoA in a home agent HA via the FA. When the home agent HA capsulates and transmits data from the MN to the CoA, the FA undoes the capsulated data and transmits the same to the MN. In this case, the FA acts a default router of the MN, for the data sent by the MN.
When the MN moves to an adjacent cell, between base stations such as a base transceiver station (BTS) of the global system for mobile communications (GSM) and a base station (BS) of the code division multiple access (CDMA), an IP address is not changed. Accordingly, only handoff of a link level occurs. Various methods such as soft handoff are provided for the handoff of a link level at high speed.
A mobile phone such as a general CDMA system, the soft handoff method is used to provide constant services while an MN moves. However, when an Internet Protocol service is provided to the mobile phone, in the case of conventional handoff, broadcasting for handoff is provided to not only a cell where the MN belongs to, but also adjacent cells. Accordingly, a lot of resources are consumed and a serious delay occurs in sending a packet because an operation of correcting location information of the MN is previously required.
To solve the above problems, U.S. Patent Application No. 2001/0036834 A1 (filed on Nov. 1, 2001) discloses a method of allowing handoff to be quick, the method in which an MN notifies a possibility of an occurrence of a handoff operation to a subnet agent, the subnet agent sends that to a mobile agent (MA), and the MA determines adjacent subnet agents of the subnet agent where the MN belongs to, set a multicast group, and multicasts for a certain amount of time while including a packet to be sent to the MN.
However, in this case, resource consumption may occur because the packet is sent to unnecessary subnet agents for a certain period of time, and head-of-line in which a control signal packet locates a data packet of a buffer and is processed later occurs because a path for the control signal for handoff uses is identical to that of data to be sent to the MN.
As a conventional high-speed handoff, in a high-speed handoff method of an IPv6 MN, when an MN moves from an existing MA to an adjacent MA, the adjacent MA allows a communication by temporarily using an unconfirmed IP address.
However, this method is very vulnerable to Dos attacks, and the MN using the un-confirmed IP address should have an ability of changing the unconfirmed IP address to another IP address when the adjacent MA notify that the unconfirmed IP address to be used is already occupied and overlapped. Also, this method is incapable of being applied to high-speed handoff of an IPv4 MN.
However, U.S. Pat. No. 6,980,802 B2 (Dec. 27, 2005) discloses an active handoff method in which an FA1 transmits IP data from a correspondent node CN communicating with an MN to an FA2 when the MN moves from the FA1 to the FA2. In this method, when the MN is out of the FA1, the FA1 transmits a message notifying the absence of the MN to a home agent HA of the MN. Also, when the MN requests the FA2 for a location registration, the FA2 transmits a location update message to the FA1 and the FA1 transmits a binding update message to the FA2.
However, in this case, when the MN requests the FA2 for the location registration, it is unclear how to know that a previous location of the MN is the FA1, and a procedure thereof is complicated.
On the other hand, U.S. Patent Application No. 2005/0114543 (filed on May 26, 2005) discloses a method capable of being applied to an MN incapable of being aware of the existence of a gateway foreign agent (GFA) more superordinate than FAs having a different address area from each other. In this case, when an MN requests a HA for a registration via an FA, the GFA is interposed between the FA and HA in such a way that the GFA adds an IP address of the GFA to an extension field of a registration request message of the MN from the FA. Also, when the MN moves from an FA of an area A to an FA of an area B, in a process of acknowledging a registration request, when the MN is already registered, the GFA responds the MN for the registration acknowledgement. Also, when the MN is not registered, the GFM generates and adds a new visitor entry in visitor list inside the GFA and sends a registration request message to an HA of the MN by adding an IP address of the GFA to an extension field of a registration request message of the MN from the FA of the area B.
In this case, though it is possible to use a general process in which an MN is registered in a normal HA, all of the HA, the GFA, and the FA should be capable of recognizing that an address of the GFA exists in an extension field of a registration request message and processing the address. Also, when an MN is not registered a new visitor entry should be generated and added to a visitor list inside the GFA before a reply for a registration request is received from an HA. The entry should be deleted when a deny message of a binding update is received, which is very complicated. Accordingly, when a reply for the registration request message from the HA is delayed while the MN moves to another FA and requests a registration, it is possible to send information while the MN is actually not registered, since the MN already exists in visitor list, which is vulnerable to a malicious call. In addition, in the described methods, there is a problem that all data packets always pass through the GFA, thereby increasing a data transfer path.
On the other hand, in a document “Stratospheric quasi-stationary platforms: (SQ-SP) complementary to radio satellite systems”, Electrical and Electronics Engineers in Israel, 1996, pp 283-286, November 1996, there is a research on whether a wireless communication method using a stationary flying object at an altitude of the stratosphere is reasonable. Generally, the research lays emphasis on power required for each frequency to transmit and receive data between a node and a high-flying object or between high flying objects and a coverage area.
Also, U.S. Pat. No. 6,167,263 (Dec. 26, 2000) discloses a platform for forming a local network using the stratosphere.
However, these methods focus on a structure of a high-flying object required for forming a local communication network using the stratosphere and controlling a location of the high-flying object. Accordingly, there is required an additional method for IP handoff of a node moving at high speed.